Oxidizable fraction

The following is an example of a typical chemical process (in a schematic form) used for the analysis of a wastewater sample in order to determine the presence of organic matter or oxidizable fraction through the measurement of the chemical oxygen demand (COD), a very common parameter in the evaluation of water pollution ... 

Step 3. Extraction of the oxidizable fraction (i.e., organic matter and sulfides) by H2O2 oxidation followed by extraction with NH4(CH3COO)... 

Oxidizable fraction of metals bound to organic matter (leaching with nitric acid and hydrogen peroxide, followed by ammonium acetate)... 

Various chemical extraction techniques have been introduced in order to selectively remove metals from the different adsorption or complexation sites of natural sediments (e.g., Tessier et al, 1979 Erel et al, 1990 Leleyter et al., 1999). It is, for example, shown by Leleyter et al. (1999) that between 20% and 60% of REE in various suspended river sediments are removed by successive extractions by water, by Mg(N03)2 (exchangeable fraction), sodium actetate (acid-soluble fraction), NH2OH - - HCl (manganese oxide dissolution) ammonium oxalate (iron oxide dissolution) and a mixture of H2O2 + HNO3 (oxidizable fraction). The complexity of... 

In general, TEs in exchangeable and acid-soluble forms are considered to be easily bioavailable (see Table 12.1). The metal-organic complex-bound form is also relatively mobile (Krishnamurti et al., 1995). The reducible and oxidizable forms are relatively stable under standard soil conditions, yet easily reducible and oxidizable fractions may be readily mobilized, as detailed in the ensuing sections. 

Hydrogen peroxide is the most popular reagent for separation of the oxidizable fraction (Hlavay et al., 2004). In general, the oxidation of soil matrix components is performed at high temperature for 2 to 3 hours as a compromise between... 

Exchangeable fraction Reduciblefraction Oxidizable fraction [ Residual fraction... 

Solvent refining to adjust the viscosity index (VI) and improve the base stock s response to oxidation. This solvent extraction separates the low VI and easily oxidizable fraction from the more desirable high VI and oxidation-resistant components. 

Oxidizable fraction binding mechanisms such as adsorption, chelating, complexation, etc. differentiation from step 3 often is impossible. 

The battle for precise, accurately determined data, has been most severe in analysing of the DOC. Depending on the method, differences by a factor 2 to 3 have been observed for samples from the same ocean areas. As is gradually becoming clear, each method is determining something different with sometimes great accuracy. Some differences depend on the composition of volatile and easily or less easily oxidizable fractions. This may even differ from area to area as well as with depth. 

Shuman (1982, 1985), working on the speciation of Cu, Mn, Fe and Zn, modified the sequence of the extraction as exchangeable, oxidizable (organically bound), easily reducible (Mn oxides-bound), moderately reducible (amorphous Fe oxides-bound), strongly reducible (crystalline Fe oxides-bound), and residual. The low percentages of the oxidizable fractions obtained following the sequential extraction scheme of Shuman (1985) as compared to those obtained following the scheme of Tessier et al. (1979) were attributed to the lack of selectivity of the method used (Charlatchka et al, 1997). 

TABLE 1 The ratio of sums of the more easily oxidizable to the more poorly oxidizable fractions of PL (XEOPL/XPOPL) and ratio of phosphatidyl choline to phosphatidylethanolamine (PC/PE) in the initial lipids of organs and formed from them liposomes in the different experiments. 

Yarlagadda et al. (1995) conducted SEM-EDS and sequential extractions on size fractionated soil specimens from sites contaminated with lead and copper by wire manufacturing (acidic pickle liquors) and steel fabrication. They found that Cu and Pb were distributed fairly uniformly across sub 2 mm size fractions. SEM-EDS showed variations between the form of contamination between size fractions. The <75 m fraction contained a few irregular shaped Cu-enriched particles and some smaller isolated Pb-enriched particles, whereas the 0.85-2.0 mm fraction contained no discrete contaminant particles. Here, lead was detected adhering to larger particles, either as small particles or as coatings. Sequential extractions indicated that Pb was primarily in carbonate and reducible phases, whereas Cu was associated with carbonate, reducible and oxidizable fractions. 

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